<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<script src="./js/index.js"></script>
<style>
    ul{
        margin: 0;
        padding: 0;
    list-style: none;
}
li{ 
    display: none;
    width: 200px;
    height: 200px;
    margin-top:10px;
    background-color: #ccc;
    
}
input.active{
    background-color: #f00;
}
</style>

<body>
    <input type="button" value="1" class="active">
    <input type="button" value="2">
    <input type="button" value="3">
    <ul>
        <li style="display:block">111</li>
        <li>222</li>
        <li>333</li>
    </ul>
</body>
</html>